An on-line monitoring device for chemical mechanical polishing

Abstract

The application discloses an on-line monitoring device for chemical mechanical polishing, which is arranged in a polishing disc and can rotate with the polishing disc. The device comprises a light source, an optical lens set for receiving a light beam emitted by the light source and generating a collimated light beam, a reflection unit for receiving the collimated light beam and reflecting the collimated light beam to form an incident light path, a detection probe arranged below a light transmission window of a polishing pad and comprising a quartz light guide tube and a single-core optical fiber, the quartz light guide tube being used for receiving the incident light path and emitting the incident light path from one end of the detection probe close to a wafer, and the single-core optical fiber being used for receiving the emitted light path reflected by the surface of the wafer; and a detector connected with the single-core optical fiber and used for receiving the emitted light path to obtain corresponding spectral information and determine the end point of wafer polishing. The light source light path from the light source to the detection probe adopts free space propagation, and the signal light path from the detection probe to the detector adopts optical fiber propagation. The propagation modes of the two light beams are well transitioned by the design of the detection probe, and high-precision detection is realized.

Description

Technical Field

[0001] This invention belongs to the field of chemical mechanical polishing technology, and in particular relates to an online monitoring device for chemical mechanical polishing. Background Technology

[0002] Chemical mechanical polishing (CMP) is a crucial process step in current semiconductor integrated circuit chip manufacturing processes. CMP uses polishing pads and polishing slurries to grind the wafer, achieving wafer surface planarization through a combination of mechanical and chemical methods. Determining the polishing endpoint is critical during the process; that is, determining when the expected amount of material removed or the desired thickness has been reached to complete the process.

[0003] Early chemical mechanical polishing (CMP) processes used grinding time to control the process endpoint, resulting in low precision and poor reliability. To adapt to the process, a series of endpoint detection methods were developed. Mechanical endpoint detection primarily monitors changes in motor torque caused by variations in material friction during the grinding process, requiring two dielectric layers with significantly different friction coefficients, thus limiting its application. Electromagnetic endpoint detection mainly monitors eddy currents generated by the metal layer on the wafer surface, applicable to metal film thickness detection but not to insulating materials. Optical endpoint detection primarily measures the intensity of light reflected from the wafer, using monochromatic lasers to monitor changes in material reflectivity during the grinding process. This requires two dielectric layers with significantly different reflectivities, and for transparent dielectric layers, the reflected light intensity is the interference intensity of the reflected light from each dielectric surface. Changes in interference intensity can provide information on the amount of material removed, but not film thickness. Spectral endpoint detection, developed from optical methods, uses multicolor, broadband, and white light sources to receive the spectral information reflected from the wafer. The correlation between spectral information and film thickness is used to monitor thickness changes, applicable to the thickness detection of transparent dielectric films. Summary of the Invention

[0004] To overcome the shortcomings of existing technologies, this invention provides an online monitoring device for chemical mechanical polishing, which combines two beam propagation methods—free space propagation and fiber optic propagation—to achieve high-precision detection.

[0005] The technical solution adopted by this invention to solve its technical problem is: an online monitoring device for chemical mechanical polishing, installed inside the polishing disc and rotating with the polishing disc, comprising,

[0006] light source;

[0007] An optical lens assembly is used to receive the light beam emitted by a light source and produce a collimated light beam.

[0008] The reflection unit is used to receive the collimated beam and reflect it to form the incident light path;

[0009] The detection probe is arranged below the light transmission window of the polishing pad, and at least includes a quartz light guide tube and a single-core optical fiber, the quartz light guide tube is used for receiving an incident light path and emitting the incident light path from one end of the detection probe close to the wafer, and the single-core optical fiber is used for receiving the emitted light path reflected by the wafer surface.

[0010] The detector is connected with the single-core optical fiber and is used for receiving the emitted light path to obtain corresponding spectral information and determine the polishing end point of the wafer.

[0011] Further, the detection probe further includes a shell, the quartz light guide tube is wrapped around the outer periphery of the single-core optical fiber, the shell is wrapped around the outer periphery of the quartz light guide tube, and the shell, the quartz light guide tube and the single-core optical fiber are arranged concentrically, or the quartz light guide tube and the single-core optical fiber are arranged adjacently, and the shell is wrapped around the outer periphery of the quartz light guide tube and the single-core optical fiber.

[0012] Further, the end faces of the quartz light guide tube and the single-core optical fiber close to the wafer are flush, and the end face of the quartz light guide tube close to the wafer has a chamfer.

[0013] Further, the chamfer is a straight chamfer with an inclination angle of 0-45°, or the chamfer is a round chamfer with a round curvature of 0-2mm. -1 .

[0014] Further, at the end of the quartz light guide tube and the single-core optical fiber away from the wafer, the single-core optical fiber protrudes from the quartz light guide tube.

[0015] Further, the outer diameter of the quartz light guide tube is 1-4mm, and the outer diameter of the single-core optical fiber is 0.1-2mm.

[0016] Further, the light source is a wide-spectrum light source with a wavelength of 200-2000nm, and the diameter of the collimated light beam is 1-10mm.

[0017] Further, the detector is a spectrometer, the detector obtains corresponding spectral information, converts the spectral information into thickness information of the medium film on the wafer surface, and determines the polishing end point of the wafer.

[0018] Further, a reference light sampling unit is arranged between the optical lens group and the detection probe, and is used for monitoring the light intensity of the light source.

[0019] Further, the reference light sampling unit includes a first beam splitter and a second beam splitter, the collimated light beam passes through the first beam splitter to form signal light and reference light, and the signal light transmits through the first beam splitter into the detection probe.

[0020] The beneficial effects of the present application are: 1) a unique detection light path system is adopted, the light source light path from the light source to the detection probe adopts free space propagation, and the signal light path from the detection probe to the detector adopts optical fiber propagation, the propagation modes of the two beams are well transitioned by the special design of the detection probe, so that the whole detection light path system can combine the advantages of the two beam propagation modes, and high-precision detection is realized; 2) most of the light intensity of the light source can fully reach the detection probe, solving the large coupling loss of the beam from the light source to the optical fiber; 3) optical fiber is used on the signal light path to collect effective signals, so that the signal collection point can be fully close to the wafer surface, and the stable transmission of the optical fiber can make the signal stably reach the detector; 4) the light emitted from the end face of the quartz light guide pipe can be focused, the aggregation of detection light energy can further increase the intensity of signal light, improve the detection precision, and the reduction of the detection area can limit the detection range of the detection probe on the wafer, and more accurately position the detection position; 5) through the unique design of the detection light path system and the probe, high precision, accurate positioning, low noise and other advantages are obtained, which is more suitable for the current process requirements; 6) online monitoring of chemical mechanical polishing is realized, the monitoring device belongs to part of the chemical mechanical polishing system, and relies on the polishing module of the CMP, rotates with the polishing disc, detects in the process of polishing and grinding, provides basis for the time point of ending polishing, and can stop polishing as soon as the polishing end point is reached; 7) the overall size is compact; 8) the signal control mode is adopted to adjust the light source and monitor the light intensity in real time, so as to ensure the stability of the measurement signal, improve the detection precision, and prolong the service life of the light source. BRIEF DESCRIPTION OF DRAWINGS

[0021] Figure 1 It is a structural schematic diagram of the chemical mechanical polishing system in the present application.

[0022] Figure 2 It is a top view of the chemical mechanical polishing system in the present application.

[0023] Figure 3 It is a perspective view of the cooperation structure of the online monitoring device and the chemical mechanical polishing system in embodiment one of the present application.

[0024] Figure 4 It is a structural schematic diagram of the part where the detection probe is located in embodiment one of the present application.

[0025] Figure 5 It is a transverse sectional view of the detection probe in embodiment one of the present application.

[0026] Figure 6 It is a longitudinal sectional view of the detection probe in embodiment one of the present application, and the chamfer is a straight chamfer.

[0027] Figure 7This is a longitudinal sectional view of the detection probe in Embodiment 1 of the present invention, where the chamfer is a rounded chamfer.

[0028] Figure 8 This is a schematic diagram of the focusing of the detection probe in Embodiment 1 of the present invention, where a represents the detection probe with a chamfer and b represents the detection probe without a chamfer.

[0029] Figure 9 The figures show the spectral reflectance curves for different film thicknesses.

[0030] Figure 10 This provides a comparison of the background spectrum (dashed line) and the signal spectrum (solid line).

[0031] Figure 11 This is a perspective view of the combined structure of the online monitoring device and the chemical mechanical polishing system in Embodiment 2 of the present invention.

[0032] Among them, 1-polishing disk, 2-polishing pad, 3-polishing slurry spray arm, 4-light transmission window, 5-polishing head, 6-wearer, 7-light transmission window path, 8-wafer, 9-light source, 10-optical lens group, 11-detector, 12-reflection unit, 13-detection probe, 131-quartz light guide tube, 132-single-core optical fiber, 133-housing shell, 134-proximal end of detection probe, 135-far end of detection probe, 136-chamfer of quartz light guide tube, 14-reference light sampling unit, 141-beam splitter. Detailed Implementation

[0033] To enable those skilled in the art to better understand the present invention, the technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only a part of the embodiments of the present invention, and not all of them. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort should fall within the scope of protection of the present invention.

[0034] Example 1

[0035] like Figure 1 As shown, in the chemical mechanical polishing (CMP) process, a polishing pad 2 is fixed on the polishing disk 1, and the polishing head 5 carries the wafer 8, ensuring the wafer 8 is in close contact with the polishing pad 2. The polishing disk 1 rotates, and the polishing head 5 rotates and reciprocates relative to the polishing disk 1, causing friction between the wafer 8 and the polishing pad 2, thus achieving mechanical polishing. The polishing slurry spraying arm 3 sprays polishing slurry through nozzles. The polishing slurry, after the rotation of the polishing disk 1, reaches the polishing head 5 and contacts the wafer 8 through the groove structure on the polishing pad 2, achieving chemical polishing. The dresser 6 dresses the polishing pad 2 to maintain its flatness and roughness.

[0036] like Figures 2-5As shown, an online monitoring device for chemical mechanical polishing is installed in the internal space of the polishing disc 1 and can rotate with the polishing disc 1. It includes a light source 9, an optical lens group 10, a reflection unit 12, a detection probe 13, and a detector 11.

[0037] Light source 9 is a broadband white light source with a wavelength of 200-2000nm. The light beam emitted by light source 9 enters optical lens group 10.

[0038] The optical mirror assembly 10 is used to receive the light beam emitted by the light source 9 and generate a collimated beam with a diameter of 1-10 mm. Specifically, the optical mirror assembly 10 consists of a series of optical lenses, which collect the light beam, reduce its diameter, and collimate it. The light beam entering the optical mirror assembly 10 is collimated into a small spot of parallel light and emitted as spatial light to the reflecting unit 12. The optical mirror assembly 10 achieves beam-constricted collimation of the light emitted by the light source 9, which solves the problem of low light intensity utilization caused by traditional fiber optic coupling, allowing a larger proportion of light energy to participate in detection, improving measurement accuracy, and reducing the power required by the light source 9.

[0039] The reflecting unit 12 is used to receive the collimated beam and reflect it to form an incident light path. In this embodiment, the reflecting unit 12 is a reflector.

[0040] The detection probe 13 is positioned below the light transmission window 4 of the polishing pad 2. The detection probe 13 includes a quartz light guide tube 131, a single-core optical fiber 132, and a housing 133. The quartz light guide tube 131 is used to receive the incident light path and emit the incident light path from the near end 134 of the detection probe 13 (defined as the end of the detection probe 13 closest to the wafer 8). The single-core optical fiber 132 is used to receive the emitted light path reflected by the surface of the wafer 8.

[0041] Specifically, such as Figure 5 As shown, a quartz light guide tube 131 surrounds the outer periphery of a single-core optical fiber 132, and a housing 133 surrounds the outer periphery of the quartz light guide tube 131. The housing 133, quartz light guide tube 131, and single-core optical fiber 132 are concentrically arranged. The outer diameter of the quartz light guide tube 131 is 1-4 mm, i.e., D1 = 1-4 mm in the figure; the outer diameter of the single-core optical fiber 132 is 0.1-2 mm, i.e., D2 = 0.1-2 mm in the figure. The inner diameter of the quartz light guide tube 131 is the same as the outer diameter of the single-core optical fiber 132, which is located at the central inner hole of the quartz light guide tube 131, and the two are concentric. The inner diameter of the housing 133 is the same as the outer diameter of the quartz light guide tube 131.

[0042] Of course, in other embodiments, the quartz light guide tube 131 and the single-core optical fiber 132 may be arranged adjacent to each other, while the outer shell 133 covers the outer periphery of the quartz light guide tube 131 and the single-core optical fiber 132, that is, the three are not arranged concentrically.

[0043] The detector 11 is a spectrometer for receiving the above-mentioned exit light path, i.e. receiving the signal light reflected by the wafer 8, so as to obtain corresponding spectral information and determine the polishing endpoint of the wafer 8. Specifically, the detector 11 is connected with the single-core optical fiber 132. As shown in Figure 10 The difference between the signal spectrum and the background spectrum represents the spectral information containing the film thickness.

[0044] As shown in Figure 6 、 Figure 7 The end face of the quartz light pipe 131 and the single-core optical fiber 132 close to the end face of the wafer 8 is flush, i.e. the end face of the proximal end 134 of the detector 11 is flush, and the end face of the quartz light pipe 131 close to the wafer 8 has a chamfer 136. The chamfer can be a straight chamfer, and the inclination angle is 0-45°, i.e. Figure 6 The angle α in the middle is 0-45°. The chamfer can also be a round chamfer, and the round curvature is 0-2mm -1 As shown in Figure 7 The end of the quartz light pipe 131 and the single-core optical fiber 132 away from the wafer 8, i.e. the distal end 135 of the detector 11, the single-core optical fiber 132 protrudes from the quartz light pipe 131.

[0045] The quartz light pipe 131 itself has the function of propagating the light beam, and it serves as a transition of the light beam in free space propagation and medium propagation, so that the sealing and stability of the entire detection system are guaranteed. Compared with Figure 8 The proximal end 134 of the detector 11 in b is flush, as shown in Figure 8As shown in Fig. 1, the proximal end 134 of the probe 11 has a chamfer 136, so that the light emitted from the end face of the quartz light pipe 131 can be focused, and the angle and curvature of the end face of the quartz light pipe can be designed according to the thickness of the light transmission window, so that the light spot can be focused on the detection surface of the wafer 8, the collection of detection light energy can further increase the intensity of the signal light, improve the detection accuracy, and the reduction of the detection area can limit the detection range of the detection probe 13 on the wafer 8, more accurately position the detection position, avoid the signal shielding caused by various patterns and micro devices on the wafer 8, and increase the effective points of detection; compared with the traditional multi-core optical fiber probe, which usually has a divergence angle of 20-30 degrees, and considering the diameter size of the optical fiber itself, the detection area often reaches several millimeters, the detection spot size of the present application can be limited to tens to hundreds of microns, and without increasing structures such as focusing mirrors in front of the detection probe, the increase of structural complexity and the surface reflection noise caused by the lens are avoided; with the further development of the wafer process, the complexity of the patterns on the wafer is further increased, and the size of the device is further reduced, so the detection accuracy of the traditional large spot cannot meet the process requirements, and the detection system proposed in the present application has the advantages of high precision, accurate positioning, low noise, etc., and is more suitable for the current process requirements.

[0046] After the above-mentioned probe 11 obtains the corresponding spectral information, it is converted into the thickness information of the dielectric film on the surface of the wafer 8 to determine the endpoint of the polishing of the wafer 8. In other embodiments, it can also be judged according to whether the characteristic spectrum, characteristic point or other signals reach the target value, which depends on the endpoint detection algorithm adopted and is not limited to the film thickness information. For example, Figure 9 As shown in Fig. 2, the spectral reflectance curves of different film thicknesses are different, so the polishing endpoint can be determined accordingly.

[0047] The working process of the present application is that the light beam emitted by the light source 9 is collected and collimated by the optical lens group 10, reflected by the reflecting unit 12 to the detection probe 13, emitted from the proximal end 134 of the detection probe 13 via the quartz light pipe 131, transmitted through the light transmission window 4 on the polishing pad 2, and irradiated to the surface of the wafer 8 pressed on the polishing pad 2, the reflected light of the surface of the wafer 8 is received by the single-core optical fiber 17 on the detection probe 16 after passing through the light transmission window 4, and reaches the detector 11; the detector 11 is a spectrometer, which receives the signal light reflected by the wafer 8 and obtains the corresponding spectral information.

[0048] This invention employs a unique detection optical path system. The light source optical path from the light source 9 to the detection probe 16 uses free space propagation, while the signal optical path from the detection probe 16 to the detector 11 uses optical fiber propagation. The two beam propagation methods are smoothly transitioned thanks to the special design of the detection probe 16, allowing the entire detection optical path system to combine the advantages of both beam propagation methods and achieve high-precision detection. Compared to the traditional Y-type optical fiber guiding technology, this invention uses free space propagation for the light source optical path, utilizes a lens group to collect and collimate the beam, and the reflection unit 12 adjusts the beam direction, ensuring that most of the light intensity from the light source 9 can reach the detection probe 13. This solves the problem of significant coupling loss from the light source 9 to the optical fiber, allowing the xenon lamp light source power to be fully utilized. Therefore, a lower-power light source can be used to meet the detection requirements, or a higher-intensity light can be used at the detection probe 13. In the signal optical path, this invention uses optical fiber to collect effective signals, ensuring that the signal collection point is close enough to the detection target, i.e., the wafer surface, and relies on the stable transmission of optical fiber to ensure that the signal reaches the detector stably. This invention combines the advantages of both free space and optical fiber transmission to improve the overall detection accuracy of the system.

[0049] Example 2

[0050] like Figure 11 As shown, this embodiment, based on embodiment one, also includes a reference light sampling unit 14, which is disposed between the optical mirror group 10 and the detection probe 13, for monitoring the light intensity of the light source 9, and includes a light intensity detector.

[0051] The reference light sampling unit 14 includes a beam splitter 141. After being emitted by the light source 9, the collimated beam emitted by the optical mirror group 10 reaches the reference light sampling unit 14 and is split into two beams by the beam splitter 141. That is, after passing through the beam splitter 141, a signal light and a reference light are formed. The transmitted beam is the signal light. The signal light passes through the beam splitter 141 and enters the reflection unit 12. The reflected beam is the reference light and reaches the light intensity detector to obtain the light intensity value of the reference light.

[0052] In addition, this embodiment also includes a controller for controlling the on / off state and light intensity of the light source 9, and calculating and determining the endpoint of the polishing of the wafer 8 based on the spectral information acquired by the detector 11. The controller is connected to the light source 9, the detector 11, and the light intensity detector. The controller can be located inside or outside the polishing disk 1 and connected to the light source 9, the detector 11, and the light intensity detector via a conductive slip ring or similar means.

[0053] The controller directly sends a control signal to the light source 9, or indirectly, the controller sends a control signal to the detector 11, and the detector 11 sends a control signal to the light source 9. The aforementioned control signals include a first control signal and a second control signal.

[0054] The first control signal is a pulse voltage value signal, the pulse width is generally 10-100us, the pulse frequency is 100-1000Hz, and the first control signal is used for controlling the light-on and light-off of the light source 9. After receiving the pulse signal, the light source 9 lights up after a certain amount of delay and turns off after a certain amount of time. The light source 9 lights up and turns off according to the frequency of the pulse signal, and the detector 11 also samples and detects according to the frequency of the pulse signal, so as to keep the synchronization of the light source 9 and the detector 11.

[0055] The second control signal is a level signal, which is a variable voltage value signal, and the voltage value is generally 0-5V. The second control signal is used for controlling the light intensity of the light source 9. After receiving the level signal, the light source 9 amplifies the voltage according to a certain proportion, and the light source 9 lights up. The higher the voltage, the greater the light intensity of the light source 9, so the size of the level signal is positively correlated with the brightness of the light source 9.

[0056] The above specific embodiments are used to explain and illustrate the present application, rather than limit the present application. Any modification and change made to the present application within the spirit and protection scope of the claims of the present application falls within the protection scope of the present application.

[0057] During the polishing process, the reference light beam can be continuously monitored by the light intensity detector to obtain the reference light intensity value. The reference light reflects the state of the light source 9. According to the reference light spectrum information and the light intensity value, the light intensity fluctuation of the light source 9 caused by factors such as aging of the light source 9 and unstable voltage can be corrected. By controlling the voltage value of the second control signal, the light intensity of the light source 9 can be maintained in a stable state, and the accuracy and precision of the film thickness measurement can be improved.

[0058] The above specific embodiments are used to explain and illustrate the present application, rather than limit the present application. Any modification and change made to the present application within the spirit and protection scope of the claims of the present application falls within the protection scope of the present application.

Claims

1. An on-line monitoring device for chemical mechanical polishing, characterized by: The detection probe is arranged below the light transmission window of the polishing pad and comprises a quartz light pipe and a single-core optical fiber. The light source is a wide-spectrum light source with a wavelength of 200-2000 nm. The collimated light beam has a diameter of 1-10 mm. The probe is a spectrometer. The reference light sampling unit comprises a first beam splitter and a second beam splitter. The collimated light beam passes through the first beam splitter to form signal light and reference light.

2. The on-line monitoring device for chemical mechanical polishing according to claim 1, wherein: The signal light passes through the first beam splitter into the detection probe.

3. The on-line monitoring device for chemical mechanical polishing according to claim 1, wherein: The chamfer is a straight chamfer with an inclination angle of 0-45°; or the chamfer is a round chamfer with a round curvature of 0-2mm -1 .

4. The on-line monitoring device for chemical mechanical polishing according to claim 1, wherein: The reference light sampling unit comprises a first beam splitter and a second beam splitter.

5. The on-line monitoring device for chemical mechanical polishing according to claim 1, wherein: The collimated light beam passes through the first beam splitter to form signal light and reference light.

6. The on-line monitoring device for chemical mechanical polishing according to claim 1, wherein: The signal light passes through the first beam splitter into the detection probe.

7. The on-line monitoring device for chemical mechanical polishing according to claim 1, wherein: ​ 8. The on-line monitoring device for chemical mechanical polishing according to claim 7, wherein: ​

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